Photosensitive resin compositions comprising, as the carrier resin component, an elastomer of, for example, chlorinated rubber, styrene-butadiene block copolymer or polyurethane, and containing an ethylenic unsaturated compound and a photopolymerization initiator are, owing to the characteristics of the elastomer therein, useful in flexographic printing plate materials; and many such compositions have heretofore been proposed in, for example, U.S. Pat. Nos. 2,948,611 and 3,024,180, and Japanese Patent Publication No. 51-43374.
Solid printing plate materials comprising such photosensitive resin compositions require developing with halogenated hydrocarbons. Therefore, photosensitive resin-containing, solid flexographic printing plate materials capable of being developed with water are desired, and some of such materials have been proposed.
In Japanese Patent Application Laid-Open Nos. 51-53903 and 53-10648, proposed are photosensitive resin compositions comprising a metal or ammonium salt of a carboxyl-having polymer. However, these compositions are problematic in that they are liquid and that they are not satisfactorily water-proof when used in printing plates. In Japanese Patent Application Laid-Open No. 61-22339, proposed is a photo-polymerizable composition comprising a salt structure as formed from a carboxyl-having copolymer and a secondary or tertiary nitrogen atom-having vinyl compound. However, this composition is also problematic in that the mechanical strength of the printing plate comprising it is poor and that the composition is difficult to form into a printing plate material having a low hardness. In order to overcome these problems, Japanese Patent Publication No. 5-6178 and U.S. Pat. No. 5,229,434 have proposed photosensitive resin compositions in which carboxyl-having microgel particles form a salt structure with ammonium. Using these compositions, it may be possible to produce printing plate materials which can be developed with water, while having good water-proofness, and which have improved mechanical strength. However, as containing microgel particles, these compositions are still problematic in that the microgel particles remain on the developed surfaces or are dropped off therefrom, thereby roughening the relief edges formed after development with water and resulting in that the image reproducibility in fine relieves is poor.